Disease selection in rice in Colombia and Central America

Materials are tested by CIAT [Centro Internacional de Agricultura Tropical, Colombia] for disease reaction prior to dispatch to national programs in Central America. Evaluations are done in Villavicencio, Colombia, a highly favorable disease environment where blast (Bl) caused by Pyricularia oryzae, leaf scald (LSc) by Gerlachia oryzae, and brown spot (BS) by Helminthosporium oryzae are endemic. It was being studied whether selecting under the high-disease environment prevalent in Villavicencio would predict disease performance in Central America and compared the efficiency of this testing with selecting entries based only on Bl bed readings. The analysis was based on disease data reported from CIAT Rice Program evaluation plots in Villavicencio and from IRTP [International Rice Testing Program] collaborators in Central America who reported moderate to severe disease levels in 1982-86 for Bl and in 1985-86 for LSc and Bs. Data for 1984 were not used because no disease evaluations from Colombia were available that year. Each line was classified as selected for a given disease when it received a score lower than that of the nearest susceptible check in the field (Standard evaluation system for rice). The coincidence in selection between Colombia and Central America was estimated for each disease as the mean probability for a line to be selected in both locations. The probability of coincidence in selection of Bl was 0.7 for 1982-83, when selection in Colombia was based on data from the uniform Bl bed in Palmira. It increased to 0.92 during 1985-86, when selection was based on field evaluations in Villavicencio. The predictability of selections done in Colombia for Central America for LSc and BS was calculated as 0.80 for 1985-86. This indicates high similarity of the race distribution of Bl and the disease environment between Villavicencio, Colombia, and testing sites in Central America